This invention relates to a Bloch-line memory device for memorizing information as a pair of vertical Bloch lines in a domain wall which surrounds a magnetic domain formed in a magnetic medium.
A Bloch-line memory device of the type described comprises a magnetic medium having a principal surface and an easy axis of magnetization orthogonal to the principal surface. The magnetic medium comprises at least one magnetic domain having a stripe shape and surrounded by a domain wall which is orthogonal to the principal surface and parallel to the easy axis. The magnetic domain has a pair of opposite end portions and an intermediate portion between the end portions.
When the Bloch-line memory device is supplied with an information signal by a magnetic field generated parallel to the easy axis, the domain wall memorizes the information signal as a pair of Bloch lines at one of the end portions. The Bloch line pair is propagated along the domain wall. On producing an output signal representative of the information signal, a magnetic bubble is generated in accordance with existence or non-existence of the pair of Bloch lines at a predetermined one of the end portions that may or may not be identical with the first-mentioned one of the end portions.
A conventional Bloch-line memory device is disclosed in Japanese Unexamined Patent Publication No. 144,487/1988 (Kokai Syo 63-144487) filed by the present assignee. In the conventional Bloch-line memory device, the magnetic medium comprises a read-out portion which is formed on the principal surface. The magnetic domain is partially expanded to the read-out portion along the principal surface parallel to the intermediate portion. The magnetic domain is chopped at the read-out portion in accordance with the number of Bloch lines in the predetermined end portion to generate a magnetic bubble. More specifically, the magnetic domain is chopped at the read-out portion to generate the magnetic bubble when the pair of Bloch lines exist in the predetermined end portion.
It is difficult with the conventional Bloch-line memory device to stably generate the magnetic bubble because the magnetic domain is expanded to the read-out portion and is chopped independent of the number of vertical Bloch lines existing at one of the end portions.